The present invention relates to the use of certain compounds to improve the lubricating properties of low sulfur-content fuels and to fuels and additive concentrates comprising the compounds.
Sulfur contained in fuel, for example middle distillate fuels such as diesel fuel and jet fuel, is said to constitute a serious environmental hazard. Hence strict regulations limiting the amount of sulfur which may be present in such fuels have been introduced. Unfortunately, fuels having a suitably low sulfur content exhibit very poor inherent lubricity and this can lead to problems when the fuel is used. For example, the use of low sulfur fuel in diesel engines frequently results in damage to the fuel injector pump which relies on the natural lubricating properties of the fuel to prevent component failure. There is therefore a need to improve the lubricating properties of low sulfur fuels.
EP-A-0608149 discloses the use of an ester as an additive in a liquid hydrocarbon compression-ignition fuel oil for reducing consumption of the fuel oil.
WO 92/09673 discloses additives which are the reaction products of (1) anhydrides and/or poly-acids and (2) aminoalcohols or amino/alcohol/amides with long chain hydrocarbyl groups attached used to improve the low-temperature properties of distillate fuels.
U.S. Pat. No. 4,617,026 (Shaub et al.) discloses the use of hydroxyl-containing esters of a monocarboxylic acid and a glycol or trihydric alcohol to reduce fuel consumption in automobiles.
U.S. Pat. No. 3,681,038 (Gaydasch) discloses middle distillate fuel compositions containing N,N-dialkylricinoleamide pour point depressants.
U.S. Pat. No. 5,194,068 (Mohr et al.) discloses fuel compositions containing small amounts of an ester of a mono- and/or poly-carboxylic acid with an alkyl alkanolamine or alkyl aminopolyalkylene glycol.
U.S. Pat. No. 4,683,069 (Brewster et al.) discloses lubricating oil compositions containing a glycerol partial ester of a fatty acid.
U.S. Pat. No. 4,491,455 (Ishizaki et al.) teaches adding esters of nitrogen containing compounds having polyhydroxyl groups with linear saturated fatty acids to fuel oils in order to improve cold flow.
U.S. Pat. No. 4,253,876 (Godar et al.) discloses corrosion inhibitors comprising triesters of an alkenyl or alkyl succinic acid or anhydride and a trialkanolamine.